Module 03: Pattern Analysis Revised

Revised pattern analysis is a system based on terms defined clearly, precisely, and lucidly, applicable to every morphologic aspect of dermoscopy. Its fundamental principle is that description should always precede analysis. Although in practice description and analysis often proceed simultaneously, logically, description must come first. This precedence becomes critically important in the assessment of difficult lesions, where the clarity gained from a full formal description may lead to a diagnosis or, at minimum, ensures all relevant differential diagnoses are considered.

Description in this context is not a "photographic" impression of the lesion's appearance. Rather, it is the extraction of features relevant to diagnosis in the simplest possible terms.

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Check Your Understanding

What are the five primary dermoscopic structural elements in the revised pattern analysis framework?

The five primary structural elements are lines (reticular, branched, parallel, radial, curved), dots, clods (globules), circles, and pseudopods. Structureless areas are also recognized as a sixth category.

All patterns observed in dermoscopy are composed of five simple geometric elements:

#	Element	Definition
(i)	Line	A two-dimensional continuous object with length greatly exceeding width, extending in one direction.
(ii)	Pseudopod	A line with a bulbous end.
(iii)	Circle	A curved line equidistant from a central point.
(iv)	Clod	Any well-circumscribed, solid object larger than a dot. Clods may take any shape.
(v)	Dot	An object too small to have a discernible shape.

Vessel morphology is described using the same objective geometric terms as pigmented structures, with additional line types defined for vessels (as these are rarely seen in pigmented structures):

Vessel Type	Description
Dots	Vessels appearing as dots
Clods	Vessels appearing as clods
Straight	Lines with no bend
Looped	Lines with one sharp bend
Curved	Lines with one gentle bend
Serpentine	Lines with multiple bends
Helical	Lines with multiple bends along a central axis
Coiled	Lines with multiple, tight bends

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A pattern is built up of multiple repetitions of the same single basic element. There is also a pattern called "structureless" -- an area characterized by the absence of any basic elements, or at least with no basic element dominating.

Key rule: One or two repetitions of a basic element are not sufficient to form a pattern. A pattern must cover a significant part of the lesion (at least 25%) and be discernible by scanning the overall appearance.

Exceptions to the 25% rule:

1. Any pseudopods or two or more radial lines are sufficient to constitute a pattern.
2. Any reticular lines not due to collision with another lesion also constitute a pattern.

The Six Line Patterns

Lines form the most common and most specific patterns in dermoscopy:

Line Pattern	Description
Reticular	Straight lines crossing each other at 90-degree angles, forming a grid.
Branched	Straight lines crossing each other at various (non-90-degree) angles.
Parallel	Straight lines that do not cross each other.
Radial	Straight lines that converge to the center of the lesion or to a central dot or clod.
Curved	Lines that bend (are not straight).
Angulated	Straight lines that do not intersect and meet at angles larger than 90 degrees, forming complete or incomplete polygonal shapes.

Fundamental Principle of Term Application

The same term is applied to patterns composed of the same type of basic element, regardless of color or diagnosis. For example:

• "Brown globules" = brown clods
• "Red lacunes" = red clods
• "Blue ovoid nests" = blue clods
• "Cobblestones" = large polygonal clods

Variations in Patterns

Variations of basic patterns may be based on:

• Morphologic appearance: e.g., reticular lines may be thin or thick.
• Distribution of basic elements: e.g., on acral skin, parallel lines may lie on ridges, in furrows, or may cross ridges and furrows.

Pigmented skin lesions may consist of a single pattern or two or more patterns. Two or more patterns can be combined in a symmetric or asymmetric fashion. Two patterns can combine symmetrically in three ways (illustrated with reticular lines and dots):

1. Dots at the periphery, reticular lines in the center.
2. Dots in the center, reticular lines at the periphery.
3. Dots scattered evenly on reticular lines.

All other combinations of two patterns will result in an asymmetric pattern.

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Check Your Understanding

How do you differentiate between dots and clods on dermoscopy?

Dots are small round structures too small to discern any further morphology (typically less than 0.1 mm). Clods (globules) are larger round to oval structures where shape can be appreciated. The distinction is primarily one of size.

Key Takeaways

• The five basic dermoscopic elements are lines, dots, clods, circles, and pseudopods (plus structureless areas as a sixth category) -- all other terms can be translated into these.
• Lines forming a reticular pattern correspond to rete ridge pigmentation, while radial lines at the periphery (streaks/pseudopods) indicate active peripheral growth.
• Dots smaller than 0.1 mm reflect melanin granules or small nests, while clods larger than 0.1 mm represent larger nests or tumor islands.

The following table translates traditional metaphoric dermoscopic terminology into simple geometric language based on the five basic elements:

Metaphoric Language	Simple Geometric Terms
Pseudonetwork	Circles, brown, and confluent
Strawberry pattern	Circles, red
Grapes	Circles, small
Blue-gray ovoid nests	Clods, blue
Comedo-like openings	Clods, brown or orange (rarely black), and circles
Cobblestone pattern	Clods, large, brown or skin colored, polygonal
Milky red globules	Clods, pink and small
Red lacunes	Clods, red
Globules	Clods, small, round, or oval
Milia-like cysts	Dots or clods, white
Peppering	Dots, gray
Annular-granular pattern	Dots, gray and circles, gray
Stars in the sky	Dots, white
Streaks	Lines
Branched streaks	Lines, branched
Brain-like appearance	Lines, curved, and thick
Fat fingers	Lines, curved, and thick
Fissures and ridges	Lines, curved, and thick
Fingerprinting	Lines, curved, and thin (plus circles occasionally)
Fibrillar pattern	Lines, parallel, crossing fissures, and ridges
Peripheral streaks	Lines, radial
Radial streaming	Lines, radial, and segmental
Starburst pattern	Lines, radial or pseudopods, peripheral
Leaf-like areas	Lines, radial, connect to a common base
Spoke wheel-like area	Lines, radial, converging to a central dot or clod
Pigment network	Lines, reticular
Atypical pigment network	Lines, reticular, and thick
Broadened pigment network	Lines, reticular, and thick
Delicate pigment network	Lines, reticular, and thin
Inverse pigment network	Lines, reticular, white or gray
Reticular depigmentation	Lines, reticular, and white
Negative pigment network	Lines, reticular, white or gray
Crypts	Lines, thick, and curved in combination with clods
Chrysalis / crystalline structures	Lines, white
Moth-eaten border	Sharply demarcated, scalloped border
Regular blotch	Structureless zone, centric
Irregular blotch	Structureless zone, eccentric
Blue hue	Structureless zone, blue
Blue-white veil	Structureless zone, blue
Milky red areas	Structureless zone, pink
Scarlike depigmentation	Structureless zone, white
Central white patch	Structureless zone, white, central

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Clinical Scenario

A 34-year-old woman presents with a 6 mm brown macule on the left thigh noticed 2 years ago. Dermoscopy reveals a single dominant pattern: thin lines crossing each other at 90-degree angles forming a grid (reticular lines), all of uniform thickness and light brown color. Small brown round structures (dots) are scattered on the lines. The overall appearance is symmetric.

What is your diagnosis and key dermoscopic findings?

Benign melanocytic nevus (junctional)

Using the revised pattern analysis framework, this lesion shows one dominant pattern (reticular lines, thin) with one color (light brown), making it symmetric by definition. The thin reticular lines correspond to a delicate pigment network -- the hallmark of benign melanocytic nevi with a junctional component. The dots on the lines are consistent with small melanocytic nests at the DEJ. A single symmetric pattern with uniform color strongly favors a benign diagnosis without need for further clue assessment.

Colors seen in dermoscopy are created by various combinations of:

• Keratin
• Melanin
• Blood (including serum in crusts)
• Collagen
• Foreign material

The color of melanin as seen by dermoscopy varies greatly depending on its localization in the epidermis or dermis:

Melanin Location	Color Seen
Stratum corneum	Black
Superficial epidermis	Dark brown
Deep epidermis / dermoepidermal junction	Light brown
Papillary dermis	Gray
Deep dermis	Blue

Other materials show less variation than melanin. Variation in color description between dermoscopists is minimized by:

1. Not describing shades of brown, gray, and other colors.
2. Classifying the number of colors only as either one or more than one color.
3. When relevant, classifying colors only as being predominantly those of melanin or predominantly not those of melanin.

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Check Your Understanding

What is a pseudopod, and what is its diagnostic significance?

A pseudopod is a bulbous projection connected to a pigmented lesion at its periphery, resembling a finger-like extension. Pseudopods indicate radial growth and are associated with melanoma when distributed asymmetrically, or with benign Spitz/Reed nevi when distributed symmetrically around the entire periphery.

Key Takeaways

• Metaphoric dermoscopy terms can be systematically translated: "pigment network" = reticular lines, "globules" = clods, "peppering" = gray dots, "crystalline structures" = shiny white lines.
• This standardized terminology reduces ambiguity and allows consistent communication across different dermoscopy schools of thought.
• Pattern recognition should always precede algorithmic analysis to ensure no structures are overlooked.

Revised pattern analysis offers a flexible framework for constructing a personal algorithm to derive as specific a diagnosis as possible for all lesions (benign or malignant, melanocytic or nonmelanocytic). It is based on the interpretation of patterns, colors, and clues.

Diagnosis follows a defined series of simple steps in logical sequence:

Step-by-Step Algorithm

Step 1 -- Describe the pattern(s): Determine the number of patterns. For analytic purposes, only two options are considered: one pattern or more than one pattern. This decision is rarely ambiguous.

Step 2a -- If ONE pattern:

• Characterize by color(s).
• A lesion with one pattern and one color is, by definition, symmetrical.
• If more than one color, assess symmetry.
• Formulate differential diagnosis based on pattern and color(s).

Step 2b -- If MORE THAN ONE pattern:

• Assess the combination for symmetry or asymmetry.
• The higher the number of patterns, the more unlikely the lesion displays symmetry.
• Analysis proceeds on the basis of the most specific pattern in the lesion, not the most prominent.
• Patterns are listed in order from most specific to least specific:

Lines > Pseudopods > Circles > Clods > Dots > Structureless
(most specific) (least specific)

• Therefore: lesions with lines are assessed by the differential diagnosis of lines. Only a lesion lacking lines is analyzed by pseudopods, and so on.
• A lesion that combines structureless with any other pattern is analyzed according to the other pattern (structureless is the least specific).

Step 3 -- Assess for clues (if needed):

• Assessment of patterns and colors may lead to a single diagnosis, but may also lead to a narrow differential.
• In that case, the lesion is examined for clues to resolve the differential.
• A clue is a feature too localized to constitute a pattern but nonetheless favoring one diagnosis over another.
• Sometimes a pattern may also constitute a clue (e.g., a structureless eccentric zone is both a pattern and a clue to melanoma).

General principle: More weight should be given to the overall pattern than to any single clue. The most difficult part of dermoscopy is correctly assigning weight to clues, particularly avoiding overvaluation of an unreliable or misleading clue. This is the role of experience.

Decision Flow

Lesion under examination
 |
 v
Describe pattern(s) and color(s)
 |
 v
 +-----+-----+
 | |
 v v
One pattern More than one pattern
 | |
 v v
Color(s)? Symmetry assessment
 | |
 v v
Symmetry? Analyze by MOST SPECIFIC pattern
 | (Lines > Pseudopods > Circles > Clods > Dots > Structureless)
 v |
Formulate v
differential Formulate differential
diagnosis diagnosis
 | |
 +------+------+
 |
 v
 Diagnosis reached?
 | |
 Yes No
 | |
 v v
 Done Examine for CLUES
 |
 v
 Resolve differential

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The authors recognize the need for a simple diagnostic system based on pattern analysis. "Chaos and Clues" simplifies the goal to identifying lesions requiring biopsy rather than reaching a specific diagnosis.

Key features:

• Applicable to every pigmented lesion.
• Does not require a decision as to whether a lesion is melanocytic.
• Detects pigmented malignancy with accuracy comparable to earlier systems.
• Tested on consecutive pigmented lesions, including significant proportions of benign and malignant nonmelanocytic lesions.

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Key Takeaways

• Six dermoscopic colors (brown, black, gray, blue, white, red) each reflect specific chromophore depths and types in the skin.
• Multiple colors in a single lesion increase the probability of malignancy because they indicate architectural complexity across skin layers.
• The presence of blue and white together (blue-white veil) strongly suggests either melanoma or Reed nevus.

Before applying "Chaos and Clues," a lesion of concern is assessed for pattern recognition morphology of any of the five common benign lesions:

1. Nevus
2. Benign keratinocytic lesion (solar lentigo, seborrheic keratosis, etc.)
3. Dermatofibroma
4. Hemangioma
5. Sebaceous gland hyperplasia

If the lesion can be identified as one of these, the algorithm is not needed. If none can be identified, the algorithmic method is applied in two steps:

Step 1: Assess for CHAOS (asymmetry of structure or color)
 |
 +----+----+
 | |
 v v
 No chaos Chaos present
 | |
 v v
 BENIGN Step 2: Search for CLUES
 (stop) |
 v
 Clue(s) found?
 | |
 Yes No
 | |
 v v
 BIOPSY BENIGN
 indicated (stop)

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Clinical Scenario

A 61-year-old man presents with a 12 mm irregular dark lesion on the upper back that has changed in color over the past 4 months. Dermoscopy reveals more than one pattern: thick reticular lines (thicker than the spaces they surround) in one area, an eccentric blue structureless zone in another, and segmental radial lines at the 7 o'clock position. At least four colors are present: brown, black, blue, and gray.

What is your diagnosis and key dermoscopic findings?

Melanoma (superficial spreading type)

Applying the pattern analysis algorithm: the lesion has more than one pattern, so we assess symmetry -- the combination is clearly asymmetric. Analysis proceeds by the most specific pattern (lines > pseudopods > circles > clods > dots > structureless). The thick reticular lines qualify as Clue 7 (lines reticular, thick -- thicker than the spaces they surround), produced by melanoma cells proliferating in the rete ridges. The eccentric blue structureless zone is Clue 1 (eccentric structureless area) and also Clue 2 (gray or blue structures). The segmental radial lines are Clue 4. Multiple clues in the presence of chaos mandate biopsy.

Chaos is defined as the presence of dermoscopic asymmetry of structure or color.

• The shape of the lesion is not relevant.
• Any color other than skin color at the edge of a lesion (such as white) should be regarded as part of the lesion.
• Lesions without chaos are not analyzed further.

Three exceptions where biopsy is indicated even in lesions lacking chaos:

1. Facial lesions with gray or blue structures.
2. Acral lesions with parallel lines on the ridges.
3. Any elevated, firm, and continuously growing lesion.

These exceptions should only be invoked in lesions that do NOT have the pattern recognition morphology of one of the five common benign lesions.

Important nuances:

• A benign seborrheic keratosis on the face may have central gray color, but symmetry, a uniform gradual border, and historical stability will confirm benign status.
• Many solar lentigines have pigmented circles, but a sharply defined scalloped border permits pattern recognition diagnosis, thus avoiding biopsy.

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In "Chaos and Clues," a clue is a feature that, when present, indicates a lesion requires biopsy. One clue is sufficient. Both chaos and the clue can be produced by the same feature.

There are nine clues to pigmented malignancy (melanoma, pigmented BCC [pBCC], and pigmented Bowen disease [pBD]):

Clue 1: Eccentric Structureless Area

• Any color except skin color.
• An asymmetrically located structureless zone favors malignancy.

Clue 2: Gray or Blue Structures

• Gray dots may be seen in pBCC, pBD, and melanoma. They are a very common finding even in noninvasive melanomas, produced by free melanin or melanin in macrophages in the dermis.
• Gray circles occur in noninvasive facial melanomas.
• Dense deposition of melanin in the dermis causes blue clods or blue structureless areas in pBCC and invasive melanomas.

Clue 3: Black Dots or Clods, Peripheral

• Peripheral black dots and clods are generally produced by melanoma cells or nests, respectively, close to or at the level of the stratum corneum due to pagetoid spread.
• Black structures are rarely seen in pigmented BCC or pBD.

Clue 4: Lines, Radial or Pseudopods, Segmental

• Radial lines may be seen at any location in BCC.
• Pseudopods or radial lines when circumferential are a feature of Reed nevus, but if segmental, they are highly specific for melanoma.

Clue 5: Polymorphous Vessels

• Vessels are called polymorphous when more than one pattern of vessel is seen.
• Polymorphous vessels reflect disordered malignant growth pattern and possibly increased metabolic demand of actively growing tumor tissue.
• If vessels as dots are present, melanoma is more likely than BCC.

Clue 6: White Lines

• To qualify as a clue, white lines must be clearly lighter than perilesional skin.

Clue 7: Lines Reticular or Branched, Thick

• To be called thick, the lines must be thicker than the spaces they surround.
• This pattern is produced by melanoma cells proliferating in the rete ridges.
• Not seen in pBCC or pBD.

Clue 8: Angulated Lines

• Straight lines that do not intersect and meet at angles larger than 90 degrees, forming complete or incomplete polygonal shapes.

Clue 9: Lines, Parallel, Ridges (Acral Skin)

• This is a clue to malignancy even in the absence of chaos.
• Subcorneal hemorrhage also produces this pattern.
• Whether pigment lies on ridges or furrows is often easier to assess at the edges of a lesion.

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Key Takeaways

• Chaos (asymmetry of structure and pattern) is the prerequisite for applying the Clues analysis; without chaos, a lesion is likely benign.
• The eight clues to malignancy include eccentric structureless areas, thick reticular or branched lines, gray or blue structures, black dots/clods in the periphery, polymorphous vessels, lines radial or pseudopods (segmental), and white lines.
• Any lesion with chaos plus at least one clue warrants biopsy or excision.

Basic Element	Appearance	Common Diagnostic Associations
Lines, reticular (thin)	Grid-like, thin lines crossing at 90 degrees	Benign melanocytic nevi (delicate pigment network)
Lines, reticular (thick)	Grid-like, thick lines (thicker than spaces)	Melanoma (atypical/broadened network), CLUE #7
Lines, reticular (white/gray)	White or gray grid pattern	Melanoma (negative pigment network), dermatofibroma
Lines, branched	Lines crossing at various angles	Melanocytic lesions; if thick, CLUE #7
Lines, curved (thin)	Thin, gently bending lines	Fingerprinting (solar lentigo, flat seborrheic keratosis)
Lines, curved (thick)	Thick, bending lines	Brain-like appearance, fat fingers, fissures/ridges (seborrheic keratosis)
Lines, parallel	Non-crossing straight lines	Acral lesions: furrows = benign; ridges = malignant (CLUE #9)
Lines, radial	Lines converging toward center	BCC (leaf-like areas, spoke-wheel areas); if segmental, CLUE #4 for melanoma
Lines, radial (peripheral/circumferential)	Radial lines around entire periphery	Starburst pattern (Reed/Spitz nevus)
Lines, angulated	Straight lines forming polygonal shapes (>90 degrees)	Melanoma on chronically sun-damaged skin, CLUE #8
Lines, white	Lines clearly whiter than surrounding skin	Chrysalis/crystalline structures, CLUE #6
Pseudopods	Lines with bulbous end	Starburst pattern; if segmental, CLUE #4 for melanoma
Circles, brown	Brown ring structures	Pseudonetwork (face), facial melanocytic lesions
Circles, red	Red ring structures	Strawberry pattern (actinic keratosis)
Circles, gray	Gray ring structures	Annular-granular pattern (facial melanoma), CLUE #2
Circles, small	Small ring structures	Grapes pattern
Clods, blue	Blue solid objects	Blue-gray ovoid nests (BCC, blue nevus), CLUE #2
Clods, brown/orange	Brown or orange solid objects with circles	Comedo-like openings (seborrheic keratosis)
Clods, large polygonal	Large, polygon-shaped solid objects	Cobblestone pattern (congenital/dermal nevus)
Clods, pink/small	Small, pinkish solid objects	Milky red globules (melanoma)
Clods, red	Red solid objects	Red lacunes (hemangioma, angiokeratoma)
Clods, small round/oval	Small, round/oval solid objects	Globules (nevi, melanoma)
Clods, black (peripheral)	Peripheral black solid objects	Pagetoid melanoma nests, CLUE #3
Dots, gray	Gray point-like objects	Peppering/regression (melanoma, lichen planus-like keratosis), CLUE #2
Dots, white	White point-like objects	Stars in the sky (milia-like cysts)
Dots or clods, white	White small objects	Milia-like cysts (seborrheic keratosis)
Structureless, centric	Central featureless zone	Regular blotch (benign nevus)
Structureless, eccentric	Eccentric featureless zone	Irregular blotch (melanoma), CLUE #1
Structureless, blue	Blue featureless zone	Blue-white veil (invasive melanoma, BCC), CLUE #2
Structureless, pink	Pink featureless zone	Milky red areas (melanoma)
Structureless, white (central)	Central white featureless zone	Central white patch (dermatofibroma)
Structureless, white	White featureless zone	Scarlike depigmentation (regression)

Clue #	Name	Description	Malignancies
1	Eccentric structureless area	Any color except skin color, asymmetrically located	Melanoma, pBCC, pBD
2	Gray or blue structures	Gray dots, gray circles, blue clods, blue structureless areas	Melanoma, pBCC, pBD
3	Black dots or clods, peripheral	Due to pagetoid spread at/near stratum corneum	Melanoma (rare in BCC/pBD)
4	Lines radial or pseudopods, segmental	Circumferential = Reed nevus; segmental = highly specific for melanoma	Melanoma (segmental); BCC (any location)
5	Polymorphous vessels	More than one vessel pattern; dots favor melanoma	Melanoma, BCC
6	White lines	Clearly lighter than perilesional skin	Melanoma, BCC
7	Lines reticular or branched, thick	Thicker than spaces they surround; from melanocytes in rete ridges	Melanoma only (not pBCC or pBD)
8	Angulated lines	Straight, non-intersecting, >90-degree angles, polygonal shapes	Melanoma (especially sun-damaged skin)
9	Lines parallel, ridges (acral)	A clue even WITHOUT chaos; also seen in subcorneal hemorrhage	Acral melanoma

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